Manufacture of polyphosphates



Patented Jan. 10, 1950 ZA3 i 7 MANUFACTURE OF POLYPH'OSPHATES AllensnGarrison, Houston, Tex., .assignor to-- TexacoDevelopment Corporation,New York, N ."Y.', a corporation oiDelaware No Drawing. ApplicationJanuary 18, 1946, Serial No. 642,109

2 Claims. (01. 23106) I 2 'lhis-invention-relates to compounds ofphosods. The compositions of the invention furtherphor-us and to amethod'of preparing them. The more possess certain-properties whichdistinguish invention especially relates to valuable phosphate them fromthe known higherlpolybasic polyphosglasses which maybe prepared simplyand -ecophates and which make them ,moredesirable for nomical1y.- ,5certain uses.

More specifically, thep-hosphate glasses are re- In accordance with thepresent invention I have lated to the -group .of-phosphor-us compoundsdiscovered that solid partially.neutralized-alkali which have cometome-designated aspolyphosmetal polyphosphate glasses :havingcompositions phates. The polyphosphates-also have beenrecorresponding-to the generaliormula ferred to as molecular-1ydehydrated phosphates. 10 Y I The principal polyphosphates and, so faras is known,-the only compositions of this class which Where M is analkali, metal. and. is greater than at-present are ofpracticalimportance are tetra- 2 can bepmduced atrehfiveiy lowtemperatures sodium pyrophosphate (NEAPQQ'Z), disod'iu mdihyin the rangef 2755 130400010 employing a dmgen Pymphosphate-(Na2H2P2O17)i SQGmm l5actant mixture-containingany=combination of alphosphate *(NflEiP-BQIP).and the material: known kali metal, hydrogemphosphomsandwoxygencommercially'as Sodlum *Etmphosphate vided one of the reactants iis-a:pyrophosphate or (NaSP 4013) an orthop'hosphate which :will onmolecular -de-' hydration yield a pyrophosphate and which-in the The.two pyrophosphates may be prepared by 29 reacting mixtureisiliquid-atsthetemperature of economical methods :suc'has the moleculardehythe reaction, and provided the-ratio of alkali metdration of.sodiumacid orthophosphates at relaal to phosphorus in themixture isthesame as the tivelyilow temperatures. on theother .hand,.to ratio ofthese elementsin the final product, that prepare sodium triphosphate orthe so-cal'ledso- M is, -n2 mols of alkali metal :tom. mob of phosdiumtetraphosphate; it .has been necessary.- to phorus. It is furtherprovided-that when one of employ methods involvingtthe use of hightemthe reactants is .an- .orthophosphate, thernixture peratures, for:example temperatures of the order shall require the removalsof waterof. molecular of '750 to 900 C. The difiiculties residing in theseconstitutionin order-Itozattain the desired product.

high temperature methods of preparation have t I have made thesurprising discoverythat :by had anadverse effect upon the commercialuse selecting the reactant materials asroutlined above of sodiumtriphosphate and .sodium tetraphossuch that the reactant mixture has anelemental phate, although these compositions have somecompositionsubstantially correspondingto'that of properties which makethem more. valuable for a partially neutralized :sait.;o:f-.a :polybasicpolymany uses than the related compositions such as phosphoric acid, themixture is in :the liquid the pyrophosphates. 3} phase at a relativelylowtemperature :as .com-

It is well known in the artthat the salts of the pared withthetemperaturesrequired in the-preshigher polyphosphates cannot beprepared satisently known methodsxforzthe production of the factorily bymaking the acids and subsequently polybasic polyphosphatecomplexes, andthat this neutralizing them with alkali carbonates or hyliquidphasemateriakmambe converted toa solid droxides. This method produces amixture of 1*? phosphate glass by cooling. It should be .notedmetaphosphates and pyrophosphates, and a good that in referringtothercompositions.describedas yield of the alkali polyphosphates isimpossible. partially'neutralized-salts .o'f polybasic polyphos- Thepresent invention is concerned with alkali phoric acids it is.notintended' to imply that such metal phosphoric acid compositionswhich are salts have previouslyloeen prepared; In fact it is solidphosphate glasses having compositions corbelieved that these:saltsarenew in the art. responding to partially neutralized salts ofthe In order :to prepare the partiallyneutralized or higher poly'basicpolyphosphoric acids; that is, tetra-hydrogen alkali 'metalpolyphosphate comthose containing more than 2 phosphorus atoms pleXes Iemploy as the starting-material any: mixper molecular formula. Morespecifically the inture of compounds which-will :meet the requireventionis concerned with compositions correments set forth. above; In.ageneral, .however, I sponding to alkali metal tetrahydrogenpolyphosprefer to startwithareactantmixture comprising phates, such asthe 1ith'ium;sodium andgpotassium either an orthophosphate; a.pyrophosphate or tetrahydrogen tri-, tetra-, penta-and heXaphosboth anda metaphosphate; an aalkali metal hyphates, the .term tetrahydrogenindicating the droxide or carbonate, or even another polyphospresence offour hydrogen atoms .per molecular phate. In order-vfor the reaction toproceed as formula. They .alsoare closely related from the desired Ihave found that the formation of the standpoint .of their chemicalandphysicalproperpartially neutralized salts .takes place through the tiesto the higher polybasic polyphosphates but, as medium ofthe-pyrophospha-te :and therefore it is distinguished from the knowncompositionsthey necessary tohavepresenta pyrophosphoric acid may. beprepared bysimple.andeconomicalmethcompound. lncarryingrout theinvention an .or-

formation of pyrophosphoric acid or an alkali metal acid pyrophosphate.Suitable orthophosphates are orthophosphoric' acid and the alkali metaldihydrogen orthophosphates.

Materials which may be used for reaction with the pyrophosphate includethe metaphosphates such as metaphosphoric acid and sodiummonometaphosphate, the polymetaphosphates such as sodiumhexametaphosphate, the polybasic polyphosphates such as sodiumtetraphosphate, and alkali metal hydroxides or carbonates.

The glassy complexes corresponding to the partially neutralized salts ofthe polyphosphoric acids may be prepared in a number of ways. Inaccordance with one manner of proceeding, pyrophosphoric acid ismaintained at a temperature at which it is in the liquid phase. Thepyrophosphoric acid may be prepared conveniently by molecularlydehydrating orthophosphoric acid. To accomplish this the orthophosphoricacid is heated to a temperature of the order of 200 to 300 C. or evenhigher. It is not necessary to complete the molecular dehydration of theorthophosphoric composition since the dehydration may be completedlater.

After the pyrophosphoric acid is in the liquid phase the metaphosphateor other material for V 7 reaction, as mentioned previously, is added inproportions selected to yield a final product of the desiredcomposition. It has generally been found that the metaphosphate, orother reactant material, will not combine with the pyrophosphoric acidat the low temperature at which the molecular dehydration of theorthophosphoric acid may be accomplished and therefore, following theaddition of the metaphosphate or other reactant material'the temperatureis preferably raised sufiicien-tly to effect liquid phase reaction ofthe materials. The temperature necessary to accomplish this will varydepending upon the specific composition of the mixture, but it has beenfound that temperatures within the range of about 2'70 to 400 C.generally will produce the desired results. 'Forexam'ple the preparationof the tetrahydrogen triphosphates may be carried out at temperatures inthe range of about 275 to 300 (3., the corresponding so-called tetraphosphates at about 350 to 360 0., the pentaphosphates at about 390 C.and the hexaphosphates at about 390 to 400 C.

In accordance with another manner of proceeding, metaphosphoric acid ismel ted and a calculated amount of an alkali pyrophosphate is added andheating continued to complete the reaction and yield the desiredcomposition. For example, 4 mols of metaphosphoric acid when melted andreacted with 1 mol of tetrasodium pyrophosphate will produce 1 mol of aglassy complex corresponding in composition to tetrasodium tetrahydrogenhexaphosphate. Or, 2 mols of metaphosphoric acid may be heated with 1mol of 'disodium dihydrogen pyrophosphat'e to produce 1 mol of a glassycomplex corresponding in composition to disodium tetrahydrogentetraphosphate.

Another importantadvantage of the present invention lies in the highdegreeof fluidity of the products at relatively low temperatures. 'I'husthe triphosphate compound is sufl'iciently liquid '4 so as to be readilymobile at temperatures as low as C. and the so-called tetraphosphate issufficiently fluid at 200 C. to permit it to be readily poured. Theso-called pentaand hexaphosphate required somewhat higher temperaturesfor an equivalent degree of fluidity but may be poured without troubleat the temperature at which they are prepared.

The liquid phase product is cooled to produce a solid phosphate glass. Ihave found that the cooling operation need not be practiced in anyspecial manner since in most cases clear water soluble glasses may beobtained either by slow cooling or by shock chilling. This isparticularly true in the case of the triand tetraphosphate compositions.In the case of the penta and hexa compositions the glassy products areinclined to become opaque and crystalline if the cooling is too slow.Even so the opaque materials are quickly and almost completely watersoluble. In order to prevent this opacity I prefer to em ploy a fairlrapid cooling procedure to obtain perfectly clear and completely watersoluble acid glasses. In any event the very rapid method of coolingknown as shock chilling is not necessary although it may be employed ifso desired.

It will be understood, of course, that this invention may be practicedin other ways, for example, when employing a pyrophosphoric compound thereactant materials may be mixed in the solid phase and then heated tothe desired liquid reaction temperature, or an orthophosphate and ametaphosphate or its equivalent may be mixed in the solid phase and theresulting mixture heated to simultaneously accomplish both moleculardehydration of the orthophosphate to the pyro state and reaction of thepyro compound with'the metaphosphate, or an orthophosphate may be meltedbut not molecularly dehydrated prior to the addition of the metaphosphate or its equivalent.

In order to fully understand the present in-" vention a number ofequations are given below for some of the possible reactions which maybe carried out. It is to be understood however that these reactions aremerely representative and are not to be construed to limit or restrictthe invention in any way.

It will be seen that the present method possesses important advantagesas compared with the high temperature methods commonly used for theproduction of the higher polybasic polyphosphates. Thus, the reactiontemperatures are considerably lower, 275 to 400C as comparedwith 750 to900 C. Moreover, while shock chilling asasgsoe is necessary in themethods usuallyr-ius'edsiior preparation *of so cium 'trlphosp'hate and;sodium tetraphosphate glassesg shock chilling is not a required featureof the present method.

The phosphate glasses "of" the invention are characterized by beingrapidlysolubleain water as compared with the known available higherpolybasic polyphosphates; they have calcium sequesteringpropertiesan'd'th'erefore'may be employedrior the treatmentofrhardwaters; and they posses-:deflocculating andzviscosityireduoingproperties-which makeoahe'mwaluable ion use in the: treatment or.preparation of aqueousxclay compositions. such as dlll-lilig"lffllld5employed. theidrillingiof oil and gasewellsnand clay-z'slips used forthe manufactureof chinaware and pottery. The compositions are clearglasses, somewhatihygroscopic, but theyJmay b handledsatisfa'ctorilylassolid materials. :They may be? neutralized with al-kalicarbonates orhydroxides in water solutions, and the neutral solutions thus obtainedare 'equivalent'to the solutions containing the same amount ofpolybasi'c polyphospl'iates prepared "by the well knownwhi'ghtemperature methods.

My invention therefore affords :an improved method of preparing neutralsolutions ofipolyba'sic polyphosphate compositicns by' Lsimple-r'r-eactions at: lower'temperatures than herefore pose sible, as Well-'asa method ofpreparingthe glassy tetrahydrogen alkali polyphosphatecomplexes which are new in the art.

In order that the invention may be understood more fully reference maybe had to the followin examples which will serve to illustrate preferredmethods and compositions of the invention:

Easample I 100 grams of commercial 85% orthophosphoric acid weremolecularly dehydrated to pyrophosphoric acid by heating in a glassbeaker at 275 C. When hydration to the pyro acid was completed, 44.2grams of insoluble sodium monometaphosphate were added and thetemperature raised to 310 C. The monometaphosphate dissolved rapidly inthe pyrophosphoric acid at this temperature to give a clear liquid melt.The melt was chilled, and a clear glass was obtained, the composition ofwhich corresponded to that of sodium tetrahydrogen triphosphate(NaHiPsOio) Example II Six mols of commercial 85% orthophosphoric acidwere heated to a temperature of 275 C. for minutes. To thepyrophosphoric acid obtained was added one mol of sodiumtrimetaphosphate. The temperature was raised to 300 C. and maintainedfor 10 minutes, after which the liquid melt was chilled to obtain aclear glass having a composition corresponding to the formula NaH4P3O1o.

Example III 40.9 grams of commercial. 85% orthophosphoric acid wereheated to 289 C. until the.

weight of the sample was reduced to 32.1 grams. To this amount of thepyrophosphoric acid was added 36.2 grams of water-insoluble sodiummonometaphosphate. The mixture was then heated to 315 C. to obtain aclear liquid melt and allowed to cool slowly to room temperature bystanding overnight. The product obtained, which had a compositioncorrespondin to that of disodium tetrahydrogen tetraphosphate'(NaiI-I4P4'Oii) v p was a clear::glassuw;h-zportionaof ithisl'gl-assyprod"- uct: was subsequently-reheated =-.to 350 i Cci'and the liquid"mert awaismhocktchilled; flh'eglass .ob=

tamed by :the'i slow cooling procedurewas ridentie cal -:torthatziobtai-ned-by shock rchilling zand -was 'equallyxas solublei: I

Erajmplc IV lost-Kby-weighingthebeaker-and the'melte The composition.ofthe =final product corresponded to that-.ioffdisodiu m tetrahydrogen::tetraphospha-te (Na2H4'P4Ql 3) Enoughwater-wasa-lost from theoriginal-orthophosphoric wacid; to. .result in its complete 1dehydration-$0 the 'pyroacid and the tetraphosphate -;is accounted iforas -the-rea-otion product from two mols of NaPOa and one mol of H4P2O7.

Example V 50 grams of commercial orthophosphoric acid were molecularlydehydrated to pyrophosphoric acid at 275 C. 44.2 grams of sodiumtrimetaphosphate were then added, and the resulting mixture heated to amaximum temperature of 310 C. The molten glass was chilled to obtain asolid glassy product having a composition corresponding to that ofdisodium tetrahydrogen tetraphosphate.

Example VI 17.2 grams of 85% commercial orthophosphoric acid weredehydrated to the pyro acid at a maximum temperature of 275 C. A 5 gramportion of lithium pyrophosphate (Li4P207) was then added withoutincreasing the temperature. The lithium pyrophosphate rapidly went intosolution to give a clear melt. To this mixture 7.97 grams ofmetaphosphoric acid was added. The molten product was chilled, and aclear glassy product obtained which has a composition corresponding tothat of lithium tetrahydrogen triphosphate, (LiH4P3O1o) Obviously manymodifications and variations of the invention, as hereinbefore setforth, may be made without departing from the spirit and scope thereof,and therefore only such limitations should be imposed as are indicatedin the appended claims.

I claim:

1. The method of preparing at temperatures below 400 C. a polyphosphateglass having calcium sequestering and viscosity reducing properties,which comprises heating a mixture of a phosphoric compound and an alkalimetal compound selected from the group consisting of the alkali metalhydroxide and the carbonate and phosphate salts thereof, at a liquidreaction temperature above 270 C. but below 400 C. until a clear liquidmelt is obtained, the total phosphorus and the total alkali metal in themixture being in the proportion of n mols of phosphorus to (n2) mols ofthe alkali metal, then cooling the melt, and separating as a final solidproduct an acid polyphosphate glass melting below 400 C. and analyzingto a composition corresponding to the formula M(1'p2)H4PnO(3n-+1), whereM is an alkali metal, and n is a whole number greater than 2, the saidcomposition having the property of being neutralized in Water solutionwith alkali metal carbonates and hydroxides to produce a neutralsolution equivalent to a water solution containing the same amount ofthe corresponding neutral polybasic polyphosphate composition.

2. The method of preparing at temperatures below 400 C. a triphosphateglass having calcium sequestering and viscosity reducing properties,which comprises molecularly dehydrating orthophosphoric acid at least inpart to pyrophosphoric acid and heating the same in a'mixture withsodium carbonate at a liquid reaction temperatureof about 275-300 C.until a clear liquid melt is obtained, the total phosphorus and thetotal sodium in the mixture being in a proportion to provide n mols ofphosphorus to (11-2) mols of sodium, then cooling the melt, andseparating as a final solid product an acid triphosphate glass meltingaround 130 C. and analyzing to a composition corresponding to theformula NaH4P3O1o, the said composition having the property of beingneutralized in water solution with sodium carbonate and hydroxide toproduce a neutral solution equivalent to a water solution containing thesame amount of NasPaOm.

ALLEN D. GARRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Huber, Z. Anorg. Allgem. Chem.,vol. 230 (1936), pp. 123-8.

Andress 8: Wust, Z Anorg. Allgem. Chem.," vol. 237 (1938), pp. 113431.

Partridge et al., J. Am. Chem. Soc.. vol. 63 (1941), pp. 454-6.

Mellor, Comprehensive Treatise On Inorganic and Theoretical Chemistry,vol. 2, Longmans Green & Co., New York (1922), p. 866.

1. THE METHOD OF PREPARING AT TEMPERATURES BELOW 400*C. A POLYPHOSPHATEGLASS HAVING CALCIUM SEQUESTERING AND VISCOSITY REDUCING PROPERTIES,WHICH COMPRISES HEATING A MIXTURE OF A PHOSPHORIC COMPOUND AND AN ALKALIMETAL COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE ALKALI METALHYDROXIDE AND THE CARBONATE AND PHOSPHATE SALTS THEREOF, AT A LIQUIDREACTION TEMPERATURE ABOVE 270*C, BUT BELOW 400*C. UNTIL A CLEAR LIQUIDMELT IS OBTAINED, THE TOTAL PHOSPHORUS AND THE TOTAL ALKALI METAL IN THEMIXTURE BEING IN THE PROPORTION OF N MOLS OF PHOSPHORUS TO (N-2) THEPROPORTION OF N MOLS OF PHOSPHORUS TO (N-2) MOLS OF THE ALKALI METAL,THEN COOLING THE MELT, AND SEPARATING AS A FINAL SOLID PRODUCT AN ACIDPOLYPHOSPHATE GLASS MELTING BELOW 400*C. AND ANALYZING TO A COMPOSITIONCORRESPONDING TO THE FORMULA M(N-2)H4PNO(3N+1), WHERE M IS AN ALKALIMETAL, AND N IS A WHOLE NUMBER GREATER THAN 2, THE SAID COMPOSITONHAVING THE PROPERTY OF BEING NEUTRALIZED IN WATER SOLUTION WITH ALKALIMETAL CARBONATES AND HYDROXIDES TO PRODUCE A NEUTRAL SOLUTION EQUIVALENTTO A WATER SOLUTION CONTAINING THE SAME AMOUNT OF THE CORRESPONDINGNEUTRAL POLYBASIC POLYPHOSPHATE COMPOSITION.